A recently observed interstellar comet, 3I/ATLAS, may be between 10 and 12 billion years old, making it one of the oldest known objects to pass through the solar system. If confirmed, the findings suggest the comet formed during the early stages of the Milky Way and could be a remnant of a long-lost planetary system.
The object is only the third confirmed interstellar visitor detected entering the solar system, following 1I/’Oumuamua and 2I/Borisov. Initial estimates based on its unusually high velocity suggested a broad age range, but new analysis of its chemical composition points toward a much earlier origin, according to Space.com.
Researchers used the James Webb Space Telescope to study the comet’s isotopic composition, focusing on the ratio of carbon-12 to carbon-13 and the presence of deuterium in its water. These measurements provide key insights into when and where the object formed. The results indicate that 3I/ATLAS contains significantly less carbon-13 than objects formed later in galactic history.
Carbon-13 tends to accumulate over time through stellar processes such as nova explosions. A low abundance relative to carbon-12 suggests the comet formed before these enrichment processes became widespread. Based on galactic evolution models, this places its formation roughly 10 to 12 billion years ago, within a few billion years of the Milky Way’s formation.
Additional evidence comes from the comet’s high deuterium content. Deuterium enrichment typically occurs in extremely cold environments, such as interstellar molecular clouds. The elevated deuterium-to-hydrogen ratio observed in 3I/ATLAS suggests it originated in a cold, early-stage region of the galaxy with relatively low levels of heavy elements.
The comet’s speed also supports its estimated age. Traveling at approximately 36 miles per second relative to the sun, it is the fastest interstellar object recorded to date. Astronomers note that such high velocities are often the result of repeated gravitational interactions with stars over billions of years, gradually accelerating the object through space.
Scientists believe comets like 3I/ATLAS form in the outer regions of planetary systems, beyond the so-called snow line where ice can persist. As such, they can preserve chemical signatures from the early stages of planet formation. The presence of water, carbon-rich compounds, and organic molecules in 3I/ATLAS indicates that these ingredients were present even in some of the earliest planetary systems in the galaxy.
Despite these insights, the comet’s exact origin remains unknown. Tracing its trajectory back more than a few million years is difficult due to gravitational interactions with stars that alter its path. However, its age suggests it may have originated in the Milky Way’s thick disk, an older region of the galaxy formed early in its history.
If confirmed, the findings imply that the star system that produced 3I/ATLAS may no longer exist. The comet would therefore represent a rare surviving fragment from a distant and early era of planetary formation, offering a glimpse into conditions that existed billions of years before the formation of the solar system.
The research is currently available as a preprint and has not yet undergone peer review, with further observations expected to refine estimates of the comet’s composition and origin.